This invention relates to vapor jet vacuum pumps and, more particularly, to vapor jet vacuum pumps and methods of operating wherein one or more ejector stages are located in a foreline conduit.
Vapor jet vacuum pumps, also known as diffusion pumps, are widely used for vacuum pumping of enclosed chambers to high vacuum. The basic components of a vapor jet vacuum pump include a housing having an inlet port and a foreline which functions as an exhaust port. The housing may include a generally cylindrical portion and a foreline conduit. The foreline conduit may be coupled to a roughing pump, or a backing pump. A vapor source in the form of a boiler assembly is sealed within the lower end of the housing. The boiler assembly includes a reservoir for a liquid, such as oil, and a heater for vaporizing the liquid. A vapor jet assembly mounted within the housing directs one or more annular vapor jets toward the housing wall, where the vapor is condensed. The condensed vapor returns to the liquid reservoir, and the cycle is repeated. The vapor jets drag gas molecules from the enclosed chamber to which the pump is attached, thereby vacuum pumping the chamber.
Prior art vapor jet vacuum pumps have utilized an ejector stage to increase the exhaust pressure of the pump. The ejector stage includes a nozzle that is mounted within the cylindrical portion of the housing assembly and is aligned with the foreline conduit. A portion of the vapor generated by the boiler assembly passes as a vapor stream through the nozzle into the foreline conduit. The stream of vapor drags gas molecules toward the exhaust port of the pump. See for example U.S. Pat. No. 4,845,360, issued Jul. 4, 1989 to Landfors.
Limiting power consumption is frequently an important issue in the operation of vapor jet vacuum pumps. Vapor jet vacuum pumps are very inefficient with respect to the work done to compress the pumped gas. At maximum throughput operation, the efficiency may be only 1% or 2%. Most energy is used for reheating and reevaporating the condensed oil vapor. Under some operating conditions, approximately half of the power consumed by the vapor jet vacuum pump may go to operating the ejector stage.
Accordingly, there is a need for improved vapor jet vacuum pumps and methods of operating vapor jet vacuum pumps.
According to a first aspect of the invention, a vapor jet vacuum pump is provided. The vapor jet vacuum pump comprises a housing having an inlet port and a foreline conduit, a vapor jet assembly within the housing, a vapor source for supplying a vapor to the vapor jet assembly, and an ejector stage including an ejector nozzle mounted in the foreline conduit and a fluid inlet located external to the housing and coupled by an ejector conduit to the ejector nozzle.
According to a further aspect of the invention, a method is provided for use in a vapor jet vacuum pump comprising a housing having an inlet port and a foreline conduit, a vapor jet assembly within the housing and a vapor source for supplying a vapor to the vapor jet assembly. The method comprises operating an ejector stage, including an ejector nozzle mounted in the foreline conduit and a fluid inlet located external to the housing and coupled by an ejector conduit to the ejector nozzle by causing fluid flow through the fluid inlet, the ejector conduit and the ejector nozzle.
According to another aspect of the invention, a vacuum pumping system is provided. The vacuum pumping system comprises a vapor jet vacuum pump comprising a housing having an inlet port and a foreline conduit, a vapor jet assembly within the housing, a vapor source for supplying a vapor to the vapor jet assembly, and an ejector stage including an ejector nozzle mounted in the foreline conduit and a fluid inlet located external to the housing and coupled by an ejector conduit to the ejector nozzle, and a backing pump coupled to the foreline conduit.